Oscillator coupling ctrctt it for heterodyne receivers



March 8, 1932. w. CARLSQN OSCILLATOR COUPLING CIFCUIT FER HE-TERODYNE RECEIVERS -Filed 0ct. "r. 1930 I Invntor: Wendell LCarlson,

His Attorney.

Patented Mar. 8 1932 WENDELL L. CARLSON,

rare cor/many, A. C(JRPORATION or NEW YORK PATENT orric g or nannonrrnnnnnw JERSEY, AssIGnoR'ro- GENERAL" Ema.

OSCILLATOR COUPLING cIfidUI'r FOR HETERODYNE RncEIvEns Application med October 7,19 0. Serial No. 487,047.

The present invention relates to heterodyne radio receiving apparatus, and more particu larly it relates to an oscillator coupling circuit for apparatus of that character. 3 5 In heterodyne receiving apparatus it is custernary to provide'an oscillation generator or oscillator adapted to deliver a relatively high oscillation voltage and to derive therefrom a relatively low voltage for beating with received signals to produce the intermediate frequency. I

The use of a high oscillation voltage has the disadvantage that precautions must be taken to prevent radiation from the oscillator which '15 would cause interference to associated or nearby apparatus, and that the coupling does not provide for uniform sensitivity over a given range of frequencies, such as the broadcast band for example.

preventing radiation from oscillators in connection with heterodyne recelvlng apparatus, including the provision of means for loading the tuned circuit of the oscillator.

25 The loading means is efiective in. reducing radiation but must be arranged to provide no appreciable initial load, in order that oscillations may be permitted to start. The control of oscillation voltage by loading has the 80 disadvantage that the load tends to change the operating characteristic and resistance of the circuit to which it is applied. However the loading principle may effectively be carried out in connection with an oscillator for it is the object of the present invention to provide an improved oscillator coupling cir-.

cuit for apparatus of that type, in which are eliminated the above-named and other disadvantages common to circuits heretofore used and which provides means for efiectively coupling the oscillator to the heterodyne detector.

Various expedients have been provided for a heterodyne radio receiving apparatus, and

The invention will better be understood.

iring diagram of an oscillator coupling circuit embodying the invention;

Referring to the drawing, 5 is aheterodyne detector of the hot-cathode electric-discharge type having a cathode 6, an anode 7 and two;- grid electrodes 8 and 9. This may be a screen grid tube in which the control electrode or grid 8 is interposed between the cathode 6 and the second control electrode or's'creen grid 9. I J p f 5 .33

. The detector is connected'in thesignal-chanml of the receiving apparatus through-the medium of a signal input circuit 10, and an output circuit 11 which servesto conduct fromthe detector the combined signal :andig; oscillation frequency, or-the' intermediate fre quency. In the present example the input circuit is connected with grid electrode 9 through a suitable tuned coupling tra'nsformer 12, and the anode 7 is connectedwitli'H-JC- the output circuit 11 through a second tuned transformer 13 representing any suitable cou ablesource suchas batteries 14, 15 and 161espectively. I

The grid electrode 8 isdirectly connected with a tuned circuit 17 of an oscillationgenerator or oscillator, which in the present ex-f ample employs as an oscillation device an electric discharge device18 having a control grid 19 connected with the tuned circuit 17 and provided with a suitable grid'condenser 20 and grid resistor 21. V The oscillator mayi be of any suitable type having an oscillatory circuit such as circuitv 17. In the present example circuit 17 includes an inductance 22 tuned by a condenser 23. 1 The oscillator device 18 receives its anode potential from the" source 16 and its cathode potential from a source 24:; r

The grid electrode 8 of the detector device 5 is connected through the oscillator tuned circuit 17 in such a manner, as indicated in the"? drawing, that it receives its potential from .thesource 14. Both of the grid'electrodes of the detector device 5 are'therefore at the same negatlvejpotential, in the present example.

It will be seen thatzthe. detector device in 'flflfl .20 from becoming excessively high and the above described circuit is connected in the signal channel, as a space charge device, since the signal is arranged to be applied to the outer grid. In the ordinary operation of a four-electrode electric-discharge device or a space charge device, the inner grid ad aCent the cathode is operated at a constant positive potential. In the present example it is operated at a positive potential during each posi- 19 tive half cycle of the voltage wave supplied by the oscillation generator, that is, during the half cycle when the oscillator gridris positive.

During the positive halt cycle, through 5 the direct coupling between the space charge V the signal frequency to the control grid 9 from r 30 the input circuit 10. A combined or intermediate trequency is therefore applied to the output circuit 11. V

The device 5 therefore operates as a combined detector and loading device, directly connected with the heterodyne oscillator tuned circuit, and has the advantage that because of the direct connection and because of the space charge operation of the detector a low generator oscillation Voltage is suitcient toapply the oscillation frequency to the electrode, said tuned circuit being connected with said grid electrode and arranged to have oscillations excited therein by said discharge device, and an electric discharge detector having an anode, a control grid, a space charge grid, and a cathode, said space charge grid being directly connected with said tuned oscillator circuit whereby said space charge grid provides a load for said oscillation generator, a source of unidirectional potential connected between said space charge grid and said cathode to impress a negative potential on said space charge grid with respect to said cathode thereby to prevent initial loading of said oscillation generator, a signal input cir'cut connected with said control grid. and a signal output circuit connected with said anode. I

In witness whereof, I have hereunto set hand this second day of October, 1930. lVENDELL L. CARLSON.

signal channel, thereby reducing the interference or radiation from the oscillator andpermitting a more uniform signal response. Furthermore, the loading of the oscillator by the detectortube is such that the oscillation strength is reduced without preventing the oscillator from starting or maintaining oscillations.

Stated in another way the above-described loaded and prevented from reaching oscillation voltages of excessively lllPll amplitude by a loading device including the space charge grid of a our element electric discharge de vicewhich serves as a detector and 1s thus directly coupled with the oscillation generator, resulting in a more uniform response, lower oscillation voltages and lower interference radiation.

What I claim as new and desire to secure by Letters Patent of the United States, is,

In a radio receiving apparatus of the heterodyne type, the combination of an oscillation generator including a tuned circuit and an electric discharge device having a grid 1 arrangement includes an oscillation generator r 

